The present invention relates to a process for preparing catalysts which are useful for hydrotreating petroleum fractions. More particularly, the present invention relates to catalysts and their method of preparation, such catalysts useful for hydrotreating petroleum fractions, and to the hydrotreatment process carried out in the presence of these catalysts.
When crude oils are distilled, the different fractions obtained contain amounts of impurities such as sulphur, nitrogen, vanadium, nickel, etc., which vary in amount with the origin of the crude. In order for further use, these fractions generally must be improved. This improvement generally is performed by a hydrogenating catalytic treatment or hydrotreatment. The additional advantage of this hydrogenating treatment is in the conversion of heavy fractions into light fractions. The catalysts which are generally used in such process consists of an oxide of a Group VIII metal, particularly cobalt or nickel, an oxide of a Group VI B metal, particularly molybdenum or tungsten and a carrier which is usually alumina. For the industrial use of such hydrotreatment processes, catalyst life should be as long as possible for economic reasons. Moreover, it is necessary that the catalyst have a high mechanical strength and a high activity.
Several processes for preparing hydrotreating catalysts are known, and their object is to obtain catalysts having a high specific surface or pores of determined sizes. However, comparative experiments with commercial catalysts generally have shown that the activity of known hydrotreating catalysts does not mainly depend on these physical properties. These experiments have shown that a prominent part is taken by the crushing strength and the abrasion strength for the catalyst life.
It has been found that catalysts in the form of beads are more resistant to deterioration than extruded catalysts. Generally, these catalysts are prepared from alumina beads by impregnating the beads with the catalytic agents. Several processes have been proposed for preparing spheroidal alumina beads. One of these consists of dispersing an alumina hydrosol as droplets, into a medium wherein gelling occurs, and thereafter, subjecting the beads which are obtained in the form of alumina hydrogel, to one or more aging treatments in order to obtain beads having a suitable mechanical resistance. According to another known process, an alumina hydrosol is mixed with an ammonium salt and a synthetic polymer or a natural gum. The mixture is then dispersed into a water-immiscible medium and thereafter subjected to an aging treatment. However, these processes have the disadvantage of requiring long treatment times, which render them uneconomic. Further, alumina beads prepared by some of these known processes contain high amounts, even excessive on occasion, of impurities which are undesirable when these beads are used as supports for hydrotreating catalysts.
An object of the present invention is to provide a new and improved method for preparing spheroidal catalyst particles on an alumina support.
Another object of the present invention is a new and improved method of preparing particles whose catalytic activity is not inhibited by impurities.
A further object of the present invention is to provide a new and improved process for preparing particles having uniform sizes.
Still another object of the present invention is to provide a process for producing hydrotreating catalysts.
A remaining object of the present invention is to provide a process for producing hydrotreating catalysts in the form of beads having a smooth surface and a high mechanical strength and a remarkable activity.